Pipe preformed liner comprising metal powder

ABSTRACT

The present invention relates to a preformed liner of tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer adhered to the surface of a pipe, and in particular, an oil well pipe, without the need for either a primer layer or an adhesive. The liner comprises an effective amount of metal powder which provides adhesion between the liner and the surface of the pipe. The present invention also relates to a process for making such pipe, where in a preferred embodiment, the liner is co-extruded to form an inner layer and an outer layer. This co-extrusion embodiment is particularly useful in applications where high purity is necessary. In this case, the inner layer comprises an effective amount of metal powder and the outer layer is pure tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer.

FIELD OF THE INVENTION

This invention relates to a preformed perfluoropolymer liner comprisingan effective amount of metal powder to cause the preformed liner toadhere to the interior surface of pipe without the need to use either aprimer layer or an adhesive. The present invention is particularlyuseful for an oil well pipe.

BACKGROUND OF THE INVENTION

Rotolining vessels to coat the interior surface of a vessel with adesired thickness of fluoropolymer is known, as disclosed in J. Scheirs,Modern Fluoropolymers, John Wiley & Sons (1997). In such a process, asufficient amount of fluoropolymer in powder form is added to a metalvessel to coat the interior surface of the vessel with the desiredthickness of the fluoropolymer, followed by rotating the vessel aboutone or more axes in an oven, to melt the fluoropolymer, whereby thefluoropolymer covers the interior surface of the vessel and forms aseamless lining. This fluoropolymer lining protects the vessel fromcorrosive materials stored or handled by the vessel, by virtue of thechemical inertness of the fluoropolymer forming the lining and of thelining being continuous with respect to the interior surface of thevessel that would be exposed to the corrosive materials if the liningwere not present. Thus, the lining is free of holes, even pinholes,through which the corrosive material could penetrate the lining toattack the material of construction of the vessel. Adherence tofluoropolymer surfaces are rare because of the non-stick property offluoropolymer, so such linings are not subject of deposition ofcomponents of conveyed materials, as may occur if the conveyed materialcools in transport, causing less soluble components to come out ofsolution. Similarly, materials conveyed in the lined vessel are notexposed to metal making up the vessel and are not thereby contaminated.The materials contact only the inert fluoropolymer surface of thelining. However, rotolining can be costly because the oven which is usedfor this process is expensive, particularly when the vessel must berotated about multiple axes.

Certain melt-processible fluoropolymers, such as copolymers of ethylenewith either tetrafluoroethylene (ETFE) or chlorotrifluoroethylene(ECTFE), on rotolining, form linings which adhere to the interiorsurface of the vessel without the used of primer or adhesive. However,for the perfluorinated melt processible copolymers, such astetrafluoroethylene/hexafluoropropylene (FEP) andtetrafluoroethylene/perfluoro(alkyl vinyl ether) (PFA), the lining doesnot adhere so well to the vessel, instead forming a “loose lining”.Loose linings are held in place by the configuration of the interiorsurface of the vessel, i.e., mechanically locked into place. While thisis satisfactory in some applications, the lack of adhesion betweenlining and interior surface of the vessel becomes disadvantageous insuch vessels as pipes, where the opportunity for mechanical restraint onmovement of the lining is limited, especially as the length of the pipeincreases. Moreover, the passage of material, such as oil through thepipe, especially when the flow of the material varies, subjects thelining to vibration and mechanical stress, which can cause the lining tocrack and fail. For corrosive materials, lining failure exposes thevessel to corrosion. For materials in which maintenance of purity iscritical, such as food processing, pharmaceuticals and semi-conductorprocessing, where contamination of the medium being conveyed by exposureto the material of construction of the vessel (i.e., metal), caused bysuch cracking and failure, is unacceptable.

Furthermore, with loose linings, gas can diffuse into the space betweenthe lining and the vessel wall, pushing the lining away from the all andrestricting material flow. This can lead to blockage and interruptedflow, which are undesirable.

Methods of lining pipes with preformed films are known, see for example,U.S. Pat. No. 2,833,686 to Sandt and Research Disclosure No. 263060,which describe liners made of polytetrafluoroethylene, which is anon-melt-processible fluoropolymer. Both of these references use afluorinated ethylene propylene bonding agent, which does not provideparticularly good adhesion because of the non-stick properties offluoropolymers generally.

A fluoropolymer preformed liner for a pipe is disclosed in U.S. Pat. No.3,462,825 to Pope. No bonding agent is used in this patent.Consequently, pressure and temperature cycling that may occur in the useof such lined pipes can cause the lining to buckle, pulling away fromthe interior surface allowing accumulation of gases and liquids betweenthe liner and the wall surface and narrowing the path of oil flow.

It would be desirable to be able to line a pipe with melt processibleperfluoropolymer thereby creating an interior surface which hasresistance to the corrosive effects of acids, and to which it isdifficult for materials to adhere, which adheres well to the pipe, andwhich does not rely on the use of bonding agents or rotolining withfluoropolymer powders. Because of its resistance to cracking andfailure, such a lining would be suitable for industries which requirehigh purity. Further there is a desire that the lining be durable andadhere well to the pipe, and not likely to buckle, when used for manyyears for conveying corrosive materials.

BRIEF SUMMARY OF THE INVENTION

With the present invention, a preformed perfluoropolymer liner is usedto line a pipe to provide a surface which is resistant to attack bycorrosive materials, and which does not contaminate the flowablematerial conveyed in the lined pipe.

Good adhesion of liner to pipe is obtained because of the presence of ametal powder in the pipe's preformed liner, which facilitates bonding ofthe liner to the surface of the pipe. It is unexpected that thepreformed liner adheres particularly well to the interior surface of thepipe in a simple heating step, without the need for an adhesive or aprimer layer. The bonding of the liner to the interior surface of thepipe involves the heating of the pipe sufficiently to melt the liner andthen cooling the pipe. The liner has a greater shrinkage during coolingthan the pipe, which would tend to pull the liner away from the interiorsurface of the pipe. Nevertheless, with the present invention, theadhesion achieved by heating surprisingly remains intact on cooling,resulting in a liner which does not pull away from the pipe's interiorsurface.

In addition, with the present invention, it is possible to line smalldiameter pipes, and small fittings and elbows, which is not possiblewith coating processes such as rotolining. This is because there is notenough room in a small pipe to accommodate the quantity of polymerparticles needed for coating the interior of the pipe. Moreover, eventhe polymer particles were forced into the pipe, the polymer must flowfreely, and there is not enough room in a small pipe for this free flow.

The present invention is lower cost than conventional rotoliningprocesses, which require use of a rotolining machine having an oven inwhich the vessel or pipe to be coated must be rotated for extendedperiods of time (see “Fluoroplastics”, Vol. 2, “Melt ProcessibleFluoropolymers”, S. Ebnesajjad, Plastics Design Library, Norwich, N.Y.,2003, p. 264). In contrast, the present invention may use a conventionaloven, or in a preferred embodiment the pipe may be rotated about asingle axis in the oven.

The present invention produces preformed liners which are particularlyuseful in high purity applications. In a co-extrusion embodiment, anouter layer which is in contact with the flowable medium is formed froma pure melt processible perfluoropolymer, i.e., a melt-processiblecopolymer of tetrafluoroethylene and perfluoro (alkyl vinyl ether) withno zinc or other metal powder present, and an inner layer is formed,which has zinc or metal powder present. With this configuration, it ispossible to get good adhesion to the pipe from a liner which does notcontaminate the flowable medium.

Because the lining of the present invention resists deposition, andbecause it has good adhesion and resists cracking and failure, it isparticularly suitable for processes which require high purity, such asfood processing, pharmaceuticals and semi-conductor processing.

Such high purity applications can be achieved in particular by aco-extrusion embodiment, in which an outer layer which is in contactwith the flowable medium is formed from a pure perfluoropolymer. Thereis no zinc or other metal powder present in this outer layer. An innerlayer which has zinc or metal powder present, is formed next to thepipe. With this configuration, it is possible to get good adhesion ofthe liner to the pipe.

Therefore, in accordance with the present invention, there is provided apipe including a preformed liner comprising a melt-processible copolymerof tetrafluoroethylene and perfluoro (alkyl vinyl ether) and aneffective amount of metal powder to cause the liner to adhere to theinterior and/or exterior surface of the pipe.

Further in accordance with the present invention, there is providedprocess for forming a pipe having a preformed liner comprising acomprising a melt-processible copolymer of tetrafluoroethylene andperfluoro (alkyl vinyl ether) and an effective amount of metal powder toadhere the liner to the interior surface of the pipe, comprising formingsaid preformed liner, inserting said liner into the pipe and adheringthe liner to the interior surface of the pipe.

The liner may also be fitted over the exterior of the pipe and the pipeand liner are heated, thereby adhering the liner to the exterior surfaceof the pipe.

According to a further embodiment of the present invention, the pipe andthe liner may be rotated about a single axis in an oven to heat the pipeand the liner and adhere the liner to the pipe. Rotation provides goodheat distribution and provides for uniform adhesion of the liner to thesurface of the pipe, eliminating buckling of the liner. Since noadhesive agent is used to hold the liner in place, rotation prevents thecollapse of the liner on itself.

According to another embodiment of the present invention, the preformedliner may be formed by co-extruding an inner layer and an outer layer.The outer layer of the liner consists essentially of, i.e., is pureperfluoropolymer of melt-processible copolymer of tetrafluoroethyleneand perfluoro (alkyl vinyl ether) and the inner layer of the liner whichadheres to the pipe comprises a mixture of a melt-processible copolymerof tetrafluoroethylene and perfluoro (alkyl vinyl ether) and a metalpowder.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a pipe including a preformed lineradhered to the surface of a pipe. While the discussion herein focuses onpreformed liners inserted inside the pipe for use where flowablematerials are conveyed in the pipe, it will also occur to those skilledin the art that the preformed liner can be inserted on the inside of thepipe, fitted as a sleeve on the outside of the pipe, as might be thecase in a heat exchanger in which cooling or heating fluid is pumpedthrough the pipe to heat or cool a fluid passing over the outside of thepipe. There may be uses in which it is useful to have both the internaland the external surfaces of a pipe covered with the liner of thisinvention.

The preformed liner is useful in reducing the corrosive effects of theenvironment and of particular materials to which the surfaces of thepipe are exposed, even though the environments and materials encounteredinside and outside the pipe may be different

The perfluoropolymer lined pipe according to the present invention mayconvey flowable media which have a high purity requirement. Such mediamay be corrosive. Such media are often encountered in industries such asfood processing, pharmaceuticals and semi-conductor processing. This isalso applicable to CPI (Chemical Processing Industry).

In addition the perfluoropolymer lined pipe according to the presentinvention may convey chemicals or oil which are subject to corrosion andare capable of plugging pipes through which they are conveyed. Anexample of such pipe is oil pipe, known as “down-hole” pipe, which isgenerally large diameter and for reasons of economy is manufactured fromcarbon steel rather than more expensive corrosion-resistant alloys.Corrosion is induced by the hot underground environment in whichdown-hole pipes convey oil from deeply buried deposits to the earth'ssurface. Materials such as water, sulfur, sulfur dioxide, carbondioxide, present in the oil typically make it acidic and capable ofcorrosive attack on the unprotected surface of carbon steel pipe. Evenat cooler temperatures, transportation pipelines that extend for longdistances at or near the earth's surface experience the effects ofcorrosion because of the long contact times involved. Corroded pipes aredifficult and expensive to replace, and present personal andenvironmental hazards.

Thus, the present invention is particularly useful with oil pipes. Suchoil pipes may be used as joined sections in an oil transportationpipeline or a down-hole oil well pipeline, it being understood, however,that the pipe of the present invention is not so limited in itsapplication. Oil pipes are generally large, having an inner diameter ofat least about 2 in (5 cm) and sometimes as large as about 6 in (15.24cm) and length of at least about 10 ft (3 m), more often at least about20 ft (6.1 m) and often a length of at least about 30 ft (9.1 m).

The pipes are typically made from rigid metal, although they could bemade of flexible metal tubing. As stated above, for reasons of economythey are usually made of carbon steel and as such are prone to corrosiveattack from acidic entities in the oil unless protected by a corrosionresistant coating. In this invention, a perfluoropolymer, which is bothcorrosion resistant and which possesses good release characteristics,covers the interior surface of the pipe. The beneficial effects of theperfluoropolymer liner of this invention are also seen for pipes thatare made from other metals such as aluminum, as well as stainless steeland other corrosion resistant alloys, on which the non-stick characterof the perfluoropolymer liner confers resistance to adhesions formingfrom components in the material conveyed through the pipe. Thedeposition of asphaltenes from crude oil is one example of suchadhesions.

While the relative dimensions of the oil pipe made in accordance withthe present invention are large, the thickness of the liner need not begreat. In an especially preferred embodiment, the preformed linertypically has a thickness from about 20 mils to about 250 mils (500-6250micrometers), preferably from about 20 mils to about 100 mil (500-2500micrometers). The large area of the interior surface of pipe over whichthe preformed liner is unsupported except by adhesion to the interiorsurface of the pipe requires high integrity for the adhesion. Otherwisethe varying conditions of temperature, pressure, and mechanical contactscould cause the liner to separate from the interior surface, leading toloss in corrosion and possibly even non-stick protection if the linerruptures. Further, separation of the liner may result in collapse of theliner causing reduced flow or even plugging.

Therefore, the preformed liner according to the present inventioncomprises a melt-processible copolymer of tetrafluoroethylene andperfluoro (alkyl vinyl ether) which provides the necessary non stickproperties to the liner and an effective amount of metal powder toadhere the liner to the pipe. The adequacy of adhesion is measured usingthe 90° Peel Test, as will be described below in the Examples. The peelstrength which can be achieved by the present invention is at least 10pounds force per inch (10 lbf/in, 1750 N/m), and preferably at leasttwenty pounds force per inch (20 lbf/in, 3500 N/m), and even morepreferably at least 25 pounds force per inch (25 lbf/in, 4400 N/m).

The metal powder is an adhesion promoting, non-bubble promoting metalpowder. Preferred metal powders that cause the preformed liner to adhereto the surface to the surface of the pipe are powders of zinc (Zn),copper (Cu), tin (Sn), or combinations thereof either as physicalblends, or as alloys. Examples of alloys include Cu/Zn (brass) and Cu/Sn(bronze). These metal powders are used in small amounts, preferably fromabout 0.1 wt % to about 10 wt %, more preferably about 0.5 wt %, toabout 7 wt %, based on polymer. The metal powder typically has aparticle size of no greater than about 100 μm, preferably less thanabout 60 μm. At least about 75 wt % and preferably at least about 90 wt% of the metal powder particles will have a particle size in the rangeof about 1 to 100 μm.

The metal powder can simply be dry blended with powder ofmelt-processible co-polymers of TFE and formed into pellets, either byphysical compacting or by melt-extrusion into a strand or stands whichare then cut to form what are known in the art as pellets, usuallyreferring to melt-cut strand, or cubes, usually referring to strand cutafter cooling. For convenience, the term “pellet” will be used toinclude both pellets and cubes. Pellets are typically about 3000-4000 μmin diameter and from about 1000-2000 μm in length. There are also“minicubes”, which are suitable for use according to this invention.Minicubes are extruded and cut like cubes, but range in length fromabout 200-2000 μm, and are about 1000 μm in diameter, as disclosed inU.S. Pat. No. 6,632,902. Minicubes are included as “pellets” as thatterm is used herein.

For most efficient dry blending, it is desirable that the metal powderand the melt-processible perfluoropolymer powder be similar in size. Fora description of melt-processible perfluoropolymer powder, see U.S. Pat.No. 4,714,756 (the heat-hardening described in that patent is notnecessary for dry blending according to the present invention). Theextruder is chosen to get adequate uniform mixing of metal powder andperfluoropolymer powder to make the metal powder-perfluoropolymer blend.This can be done with single-screw extruder or a twin-screw extruder,the latter giving better mixing if this should be necessary. Screwdesign, such as the presence of mixing elements, can also be chosen tooptimize mixing without over working the polymer.

“Powder” as used in the preceding paragraph includes the term “bead”,sometimes used for fluoropolymer intended for rotomolding applicationsas disclosed in U.S. Pat. No. 4,714,756. Particle size of powder istypically less than about 500 μm.

Alternatively, metal powder may be dry blended with already-pelletizedperfluoropolymer and fed to an extruder to make pellets of the blend ofmetal powder and perfluoropolymer. The dry blending is done at roomtemperature. With the greater disparity in size of perfluoropolymerpellets and metal powder, better mixing in the extruder may benecessary.

The metal powder-perfluoropolymer blends described in the precedingparagraphs may be of a composition rich in metal powder so that theresulting pellets can be used as “concentrate” which can be “let down”by mixing with additional perfluoropolymer (containing no metal powder)in making perfluoropolymer liner with the desired amount of metalpowder. In the case of concentrate, the amount of metal powder in thepellets can exceed the 10 wt % described above as the preferable maximumfor the perfluoropolymer liner.

It is not necessary to pelletize the metal powder-perfluoropolymer dryblend before making the perfluoropolymer liner. If desired, the dryblend may be directly extruded to make the perfluoropolymer liner.

If it is desirable to stabilize the copolymer with a fluorinationtreatment, as will be described below, such treatment is performed priorto dry blending, so that the fluorine does not react with the metalpowder. The preformed liner of the present invention comprises, inaddition to the metal powder, a melt-processible copolymer oftetrafluoroethylene and perfluoro (alkyl vinyl ether).

By melt-processible it is meant that the polymer can be processed in themolten state, i.e., fabricated from the melt into shaped articles suchas films, fibers, and tubes etc. that exhibit sufficient strength andtoughness to be useful their intended purposes. Examples of suchmelt-processible copolymers of tetrafluoroethylene (TFE) and at leastone perfluorinated copolymerizable monomer (comonomer) present in thepolymer in sufficient amount to reduce the melting point of thecopolymer substantially below that of TFE homopolymer,polytetrafluoroethylene (PTFE), e.g., to a melting temperature nogreater than about 315° C. Comonomers used in this invention areperfluoro(alkyl vinyl ether) (PAVE) in which the linear or branchedalkyl group contains 1 to 5 carbon atoms. Preferred PAVE monomers arethose in which the alkyl group contains 1, 2, 3 or 4 carbon atoms. Theresulting TFE/PAVE copolymers are commonly referred to as PFA polymer.The copolymer can be made using several PAVE monomers. In the case ofTFE/perfluoro(propyl vinyl ether/perfluoro(methyl vinyl ether)(TFE/PPVE/PMVE) copolymer, the manufacturer refers to the polymer asMFA. Preferred perfluoropolymers according to this invention PFA(TFE/PAVE copolymer), TFE/HFP/PAVE wherein PAVE is PEVE and/or PPVE(this terpolymer made for commercial use generally has a greater weightpercent HFP content that PAVE content, and is often considered a memberof the FEP family of copolymers) and MFA.

The melt-processible copolymer is made by incorporating an amount ofcomonomer into the copolymer in order to provide a copolymer whichtypically has a melt flow rate of about 0.1-100 g/10 min as measuredaccording to ASTM D-1238 at the temperature which is standard for thespecific copolymer. Preferably the melt flow rate is 0.5 to 50 g/10 min.Typically, the melt viscosity will range from about 10² Pa·s to 10⁶Pa·s, preferably about 10³ to 10⁶ Pa·s measured at 372° C. by the methodof ASTM D-1238 modified as described in U.S. Pat. No. 4,380,618.

The perfluoropolymer of this invention is preferably nonelastomeric,that is it is perfluoroplastic, and has a melting point at a heat offusion of at least about 3 J/g, preferably at least about 9 J/g. This ismeasured by differential scanning calorimetry (DSC). ASTM D-3418describes the method.

The melting temperature of the liner will vary according to itscomposition. By melting temperature is meant the temperature at the peakof the melting endotherm obtained by DSC analysis. By way of example,tetrafluoroethylene/perfluoro(propyl vinyl ether) copolymer melts atabout 305° C. Tetrafluoroethylene/perfluoro(methyl vinylether)/perfluoro(propyl vinyl ether) copolymer (MFA) has a melting pointin between these melting temperatures, generally about 290° C.

The perfluoropolymer according to this invention may have unstable endgroups which on heating can decompose to volatile product, such ascarbon dioxide and hydrogen fluoride, which can cause bubbles and voidsduring extrusion. Polymer prepared by aqueous polymerization tends tohave unstable end groups. Polymer made by nonaqueous polymerization (onemethod is described in U.S. Pat. No. 5,981,673) using suitable initiatorhas few or no unstable end groups and does not need further treatment toreduce the concentration of unstable end groups.

As described in EP 0 226 668 and in U.S. Pat. No. 4,743,658, thecopolymer may be stabilized by exposing the copolymer particles tofluorine for a sufficient time to reduce the unstable end grouppopulation in the copolymer to less than about 80/10⁶ carbon atomspresent in the copolymer. This fluorine treatment can be used on thecopolymer particles used in the present invention to reach the sameendpoint, less than about 80 unstable end groups/10⁶ carbon atoms,preferably less than about 50, more preferably, less than about 10, andeven more preferably less than about 3 unstable end groups/10⁶ carbonatoms. Examples of unstable end groups are —COOH, —CONH₂, —CH₂OH,—CO₂CH₃, —CF═CF₂, and —COF. The exposure of these end groups to fluorineconverts these unstable end groups to the very stable —CF₃ end groups.The analysis for unstable end groups is disclosed in U.S. Pat. No.4,743,658.

The preformed liner is preferably made by extruding the perfluoropolymerand metal powder, preferably blended and pelletized in a preceding stepas described above. Extrusion is done preferably using a die to make thepreformed line, usually in the form of a tube if a circular pipe is tobe lined. The outer diameter of the tube is chosen with the dimensionsof the pipe and method of bringing the pipe and liner together in mind.The preformed liner could also be made by rotomolding.

In applications where purity of the flowable medium is important, amultilayer liner can be made by coextrusion. The layer that will contactand adhere to the pipe, referred to herein as the “inner layer”,contains the metal powder described above. The layer that will contactthe flowable medium, referred to herein as the “outer layer”, containsno metal powder or other matter apart from the perfluoropolymer. Thusthe perfluoropolymer contacting the flowable medium is perfluoropolymeronly, and contains no nonfluoropolymer contaminants that mightcontaminate the flowable medium. The perfluoropolymers that make up theinner and outer layers are preferably of the same general monomercomposition for best adhesion between the layers. It is not necessarythat compositions be exactly the same, but the closer they are thebetter for interlayer adhesion. The viscosities (as measured by meltflow rate) of the polymers that make up the inner and outer layers neednot be the same so long as the polymers can be successfully coextruded.The inner layer of the preformed liner adheres to the surface of thepipe, and the outer layer adheres to the preformed liner, therebyforming a thick adherent overall lining on the surface of the pipe.

The outer layer copolymer need not be stabilized such as by fluorinationor humid heat treatment, but is preferably stabilized so as to providethe most chemically inert surface in contact with the medium containedin the pipe being lined. The copolymer can be stabilized by fluorinetreatment as described above.

The thickness of the liner for lining the interior of a pipe will bedependent on diameter of the pipe as well as for the intended use of thepipe. Preferably the thickness of a single layer is from about 2 mils toabout 500 mils. The liner may be comprised of multiple layer each layerhaving a thickness of 2 mils to 500 mils. In a preferred embodimentcomprising 3 layers, the first layer of the liner has a thickness offrom about 25 mils to 90 mils, the second layer has a thickness of fromabout 50 mils to 180 mils, and the third layer has a thickness of fromabout 50 mils to 180 mils greater than the thickness of. In a multilayerliner, the inner layer of the preformed liner can be thin relative tothe outer layer of the liner.

In a preferred embodiment, the preformed liner includes a plurality ofbarrier particles that are relatively inert to chemical attack by theflowable medium to which the pipe will be exposed. The particles form amechanical barrier against permeation of water, solvent and gases, suchas oxygen, through the liner to the surface of the pipe. Particles arepresent in the amount of about 0.5 to about 10% by weight based on thetotal dry weight of the preformed liner. Such particles tend to align inthe making of the preformed liner during conventional extrusionprocesses and contribute to the permeation resistance of the liner.Since oxygen, solvent and water cannot pass through the particlesthemselves, the presence of the aligned particles further reduces therate of permeation through the preformed liner by increasing the pathlength from the outer (exposed to the flowable medium) surface of theliner to the inner (in contact with the pipe surface) surface of theliner. In a particularly preferred embodiment, where the preformed lineris co-extruded, the barrier particles are included in the inner layer.Alternatively, an intermediate layer, which is part of the preformedliner, containing barrier particles can be extruded between the innerlayer and the outer layer of a multi-layer preformed liner.

Preferably the particles are platelet-shaped particles. Examples oftypical platelet shaped filler particles include mica, glass flake andstainless steel flake. The platelet shaped particles are preferably micaparticles, including mica particles coated with an oxide layer like ironor titanium oxide. These particles have an average particle size ofabout 10 to 200 μm, preferably 20-100 μm, with no more than 50% of theparticles of flake having average particle size of more than about 300μm. The mica particles coated with an oxide layer are described in U.S.Pat. Nos. 3,087,827 (Klenke and Stratton); 3,087,828 (Linton); and3,087,829 (Linton). The micas described in these patents are coated withoxides or hydrous oxides of titanium, zirconium, aluminum, zinc,antimony, tin, iron, copper, nickel, cobalt, chromium, or vanadium.Mixtures of coated micas can also be used.

In alternate embodiments, other particles can be included in thepreformed liner. Such particles confer improved rigidity evidenced bybetter tensile and elongation properties, improved wear resistanceand/or reduced thermal dissipation. One preferred type of particle is aceramic hollow micorsphere such as Zeeospheres G850 supplied by 3MCompany. Another preferred particle is a fiber of aromatic polyamidesuch as DuPont Kevlar® or DuPont Nomex® aramid fibrids, pulp, or floc.

In the following discussion of the insertion of the preformed line intothe pipe, the surface of the preformed liner that contacts the surfaceof the pipe is the “inner surface”. The surface of the preformed linerthat contacts the flowable material in the finished lined pipe, is the“outer surface”.

A pipe is made according to the process of the present invention in thefollowing manner. Typically the as-manufactured and supplied pipe, suchas an oil pipe, will have a coating of preservative (rust inhibitor) onthe interior, relatively smooth surface to resistance rust. The pipeinterior surface may be cleaned and then roughened, for instance by gritblasting, thereby ridding such surface of contaminants that couldinterfere with adhesion and providing a more adherent surface for theprimer layer if used and for the preformed film. Conventional soaps andcleansers can be used. The pipe can be first cleaned by baking at hightemperatures in air, temperatures of 800° F. (427° C.) or greater. Thecleaned interior surface is then preferably grit blasted, with abrasiveparticles, such as sand or aluminum oxide, or can be roughened, such asby chemical etching, to form a roughened surface to improve the adhesionof the preformed liner. The grit blasting is sufficient to remove anyrust that may be present, thereby supplementing the cleaning of theinterior surface. The roughening that is desired for adhesive adhesioncan be characterized as a roughness average of 1-75 μm Ra as measuredaccording to ASTM F-1438.

In accordance with the present invention, the liner is inserted into thepipe. There are several common techniques for doing this. In a “slipfit” embodiment, the preformed liner is tubular, with the outer diameterof the tube being slightly smaller than the inner diameter of the pipeto be lined. This allows the liner to be freely slipped into the pipe.Upon heating, the liner expands and adhere firmly to the inside of thepipe.

In certain other embodiments, the preformed liner is tubular, with theouter diameter of the tube being greater than the interior diameter ofthe pipe to be lined. In a preferred embodiment the initial outerdiameter of the preformed liner is about 10 to 15% greater than theinner diameter of the pipe. In a more preferred embodiment, thepreformed liner is applied to the interior surface of the pipe accordingto the teachings of U.S. Pat. No. 3,462,825 (Pope et al.) by grippingone end of the liner, stretching it and thereby reducing its outerdiameter, and then pulling the liner into the oil pipe mechanically.When the liner has been inserted, tension is released and the linerexpands into tight engagement with the interior surface of the pipe. Apreferred method for reducing the outer diameter is to pull the linerinto the oil pipe through a reduction die as taught in Pope et al.Alternative means of reducing the diameter of the tubular liner suchthat it could be pulled into the oil pipe of smaller inner diameterinclude 1) pulling the tubular liner under tension such that the lengthof the liner increases and the diameter of the liner decreases asdescribed in U.S. Pat. No. 5,454,419 to Vloedman or 2) pulling thetubular liner through diameter reducing rollers similar to thosedescribed in Canadian Patent No. 1241262 (Whyman et al.). In eithercase, once the tubular liner is inserted in the oil pipe, it is releasedallowing the liner to expand into tight engagement with the interiorsurface of the pipe.

An alternate method of producing a lined pipe is called swaging. In thisembodiment, the preformed film is preferably in the shape of tubularliner with the outer diameter of the tube being less than the interiordiameter of the pipe to be lined. In a preferred embodiment, the initialouter diameter of said tubular liner is about 10 to 15% less than theinner diameter of the pipe. Swaging involves mechanically reducing thediameter of a steel pipe around a liner by use of a swaging device suchas an Abby Etna Rotary Swager which applies an abundant amount of forceto the pipe through hammering, for example applying 2400 blows perminute to cause the pipe to fit around the liner. After the liner isinserted and the pipe is “swaged” down around the liner, the pipe isheated.

After the liner is inserted in the pipe, the pipe is then heated inorder to adhere the inner surface of the liner to the interior surfaceof the pipe. The pipe is heated by either oven heating or inductionheating, or other heating method. In a preferred embodiment, the oven isequipped with a rotating axis such that the pipe is rotated to achieveeven heat distribution, such as, for example, in a rotolining machine.For example, exposure to any heat source sufficient to heat or incertain cases melt only the liner's outer layer (contacting the pipe)without melting the remainder of the liner would be suitable. Thesecould also include but are not limited to, for example, flame treatingand high temperature electrical resistance furnaces. Still other heatsources which can be used include the heat from a gas fired indirectheater. A very short duration heat source would also accomplish theobjective. Detailed examples of such intense heat sources would includebut are not limited to oxyacetylene torches and heating elements ofmolybdenum disilicide (available as Kanthal Super 33 heating elementsfrom Kanthal Corporation, Bethel, Conn.). In such an arrangement, veryaccurate temperature control could be achieved. This is because modestchanges to the oven temperature would result in small temperaturedifferences at the liner inner surface. The required oven temperaturewould then be determined empirically by adjusting the speed at which thepipe moves through the heated zone and the temperature of said zone.

This technique has been successfully applied to production ofmonofilaments (see, e.g. U.S. Pat. Nos. 4,921,668, Anderson, et al. toDuPont and 5,082,610, Fish, et al. to DuPont) but has not been appliedto lining pipes until now. These and other such changes in heatingmechanism may all be made without departing from the spirit of thisinvention.

When induction heating is used, instead of heating in an oven, heat isapplied to the outside of the pipe to heat the pipe. Induction heatingof a metallic component is achieved by passing high-frequency electriccurrent through a coil surrounding a workpiece. This in turn induces ahigh-frequency electromagnetic field in the piece. The magnetic fieldinduces currents in the workpieces and the electrical resistance of thepiece to the flow of current causes the piece to heat up.

The heat in the pipe is sufficient to cause the liner to expand againstthe interior surface of the pipe and adhere the liner to the surface ofthe pipe. The maximum pipe temperature varies according to theparticular copolymer being used, and may go up to 760° F. (404° C.),with the lower end of this temperature range being 690° F. (366° C.).Time for adherence will be dependent on the heating temperature used,but the time of exposure to the maximum temperature is typically in therange of 40 minutes to 5 hours. When induction heating is used, the timeof exposure to the maximum temperature is typically in the range ofseconds.

In the induction heating process of the present invention, the pipemoves in proximity to an heating induction coil at a scanning rate ofabout 1-30 inches per minute (2.5-75 cm/min), preferably about 10-20inches per minute (25-50 cm/min). Alternatively, an heating inductioncoil may be moved in proximity to the pipe at these scanning rates.

According to the process of the present invention, after the heatingstep, the pipe is then cooled. The cooling rate may be controlled indifferent ways. Options for cooling include 1) room temperature aircooling or 2) via cooling rings, water jets, etc.

With the present invention, the pipes can be moved along the heatinginduction coil, or vice versa, so that one can process large pipeswithout the need for a bulky, standard convection oven, which isrequires a large capital investment. Moreover, the process of thepresent invention allows the liner to be adhered in the field, allowingfor on-site construction or repair, which significantly increases theflexibility of applying a liner.

When the liner is applied to the interior surface of the pipe, theexpansion of the preformed liner during the heating step, whiletheoretically greater than the expansion of the pipe, is constricted bythe pipe (when the liner is being applied to the inside of the pipe) andalso is limited by the relaxation effect of the heating of the liner tothe molten or near molten condition. As the pipe cools, there is atendency for the preformed liner to shrink. The shrinkage of the linerduring cooling starts from this relaxed condition and then outpaces theshrinkage of the pipe. Under this condition, it is surprising thatadhesion of the liner is maintained during cooling. Unexpectedly, theadhesion between the pipe and the preformed liner is sufficient toprevent the liner from pulling away from the pipe. In the presentinvention, the expansion fit of the prior art for lining a pipe isimproved by the liner having a metal powder. The resulting linerwell-adhered to the pipe resists the separation and bucklingcharacteristic of liners which do not include such powders.

In the embodiment where the preformed liner is applied to the exteriorsurface of a pipe, the preformed liner is tubular with the outerdiameter of the tuber being slightly greater than the exterior diameterof the pipe to be lined. For such an embodiment, the tubular liner maybe fitted over the pipe as a sleeve, followed by heating and cooling asdescribed above.

In prior art systems where adhesion of a liner is poor, gas is able topermeate through the liner to corrode the pipe in the cases where thegas is corrosive, such as with sulfur dioxide, and to exert pressure onthe inner surface of the liner. This results in blistering and eventualbuckling of the liner to constrict and possibly block the interior ofthe pipe. Pipes of the present invention are able to resist theaccumulation of fluids (gases and/or liquids) that might permeatethrough the liner and prevent thereby the accumulation of material atthe interface of the pipe and the liner. This greatly retardingcatastrophic failure. Moreover, the preformed liner of the presentinvention is sufficiently thick and defect-free so as to minimize thepassage of corrosive material to the surface of the pipe.

Therefore, for all of the foregoing reasons, pipes of the presentinvention are able to withstand the harsh conditions of oil production.These pipes are able to withstand typical reservoir conditions that areat least about 250° F. (121° C.) and 7,500 psi (52 MPa), with 275° F.(135° C.) and 10,000 psi (69 MPa) being quite common. The pipes of thepresent invention are also able to withstand conditions as high as 350°F. (177° C.) and 20,000 psi (138 MPa) present in some hightemperature/high pressure reserves. Higher melting perfluoropolymer,PFA, is preferred as the perfluoropolymer for the preformed liner inhigh temperature service such as this.

The invention is also applicable to pipe used in the Chemical ProcessingIndustry (CPI), especially in those applications which require highpurity and those applications where temperatures such as those describedabove are encountered. In the CPI temperatures of at least about 350° F.(177° C.) and even as high as 400° F. (204° C.) are used. The pipes ofthe preferred embodiment of this invention show superior permeationresistance to corrosive chemicals due to both to their construction,i.e., thick preformed liner, and their strong adherence to the interiorsurface of the pipe. The lined pipes of the present invention are ableto withstand the above described conditions for continuous service,e.g., for at least about 30 days, preferably at least about 60 days, andmore preferably at least about 12 months.

The preformed liner is impermeable to the corrosive materials present inthe oil and presents a nonstick surface to the oil, whereby the organicmaterials present in the oil that become insoluble as the oil cools, donot stick to the liner and restriction of oil flow and plugging isavoided. Therefore the preformed liner of the present invention is ableto provide insulation to the oil pipe to mitigate the change from hotunderground conditions to cooler earth surface effects, therebyresisting the deposit of the insoluble organic and inorganic materials.In addition, the preformed liner of the present invention possessesincreased abrasion resistance to sand and rock contained in the oil andto effects of tools scraping on the interior surface of pipe as theseinstruments are being lowered into the well for various measuring orservicing operations. The preformed liners of this invention resist bothpenetration and wear.

Because of all the above-noted advantages, the present invention iscapable of reducing the deposition of at least one of asphaltenes,paraffin wax and inorganic scale by at least about 40%, preferably atleast about 50%, as compared to the interior surface of said oil pipewithout said lining being present. These reductions are also made incomparison to pipe lined with only an epoxy resin on the interiorsurface of the pipe. In fact, reductions of at least about 60%, about70%, about 80% and even at least about 90% have been realized.Preferably these reductions apply to at least two of the depositionmaterials, and more preferably, to all three of them. Thus, with thepreformed liner of the present invention, deposition in an oil well pipeof at least one of asphaltenes, paraffin wax, and inorganic scale may bereduced by at least about 40% as compared to the interior surface ofsaid oil pipe without the liner being present. In addition, thepreformed liner provides corrosion protection to the interior surface ofthe pipe.

Test Method Adhesion Testing

Adhesion testing is performed using a ASTM D 3167 “Standard Test Methodfor 90 Degree Peel Test of Adhesives. The test apparatus is the same asdescribed in the ASTM.

This apparatus allows for a 90° angle to be maintained between thepreformed liner and the substrate (the carbon steel pipe) during theentire test. The test specimens are ½″ (1.3 cm) wide strips cutvertically from the sample pipes.

Specimens of preformed lined carbon steel pipes of approximately 4″ (10cm) inner diameter (ID) are sliced to do the adhesion tests. The testspecimens are each about 12 in long. Peel strength (lbf/in) is measuredover at least 3 inches, (disregarding at least the first 1 inch of thepeel as suggested in ASTM D 6862-04) and is reported as an averagevalue. Good adhesion is considered to be a minimum of 10 lbf/in. (10lbf/in, 1750 N/m).

EXAMPLES Fluoropolymer Resins

FP 1 is PFA: TFE/PPVE copolymer resin containing 3-4.5 wt % PPVE havinga melt flow rate of 5-7.5 g/10 min and an average particle size of about350-400 micrometers.FP 2 is PFA: TFE/PEVE copolymer resin containing 5-8 wt % PEVE having amelt flow rate of 14-23 g/10 min and an average particle size of about800 micrometers. FP3 is PFA: TFE/PPVE copolymer resin containing 3-4.5wt % PPVE having a melt flow rate of 14-22 g/10 min and an averageparticle size of ⅛″/125 mils (3.2 mm) (pellets).FP 4 is PFA: TFE/PPVE copolymer resin containing 3-4.5 wt % PPVE havinga melt flow rate of 5-7.5 g/10 min and an average particle size of⅛″/125 mils (3.2 mm) (pellets).FP 5 is PFA: TFE/PPVE copolymer resin containing 3-4.5 wt % PPVE havinga melt flow rate of 1.5-3.2 g/10 min and an average particle size of⅛″/125 mils (3.2 mm) (pellets).FP 6 is PFA: TFE/PPVE copolymer resin containing 3-4.5 wt % PPVE havinga melt flow rate of 5.0-7.5 and an average particle size of 400 microns(0.4 mm) (beads).

Example 1

A preformed-PFA liner is made using FP-1 resin by dry blending PFApowder with 1 wt % zinc powder and forming the lining by means ofrotomolding the resin into a tubular liner in a carbon-steel pipe towhich a release agent, such as FreeKote 700 NC manufactured by HenkelLoctite Corp has been applied. For this example, a pipe having an ID of4″ is filled with the PFA/Zn powder blend. Endcaps are used to containthe powder in the pipe. The pipe is placed in a conventional rotomoldingmachine where it is heated at 700° F. (371° C.) for 30 minutes whilerotating about 2 axes to make the preformed liner. The preformed lineris then released from the pipe. The outer diameter of the preformedliner is approximately the same as the inner diameter of the pipe.Although one could make a preformed liner by rotomolding, it is expectedthat it would be more economical to extrude preformed liners and themethod used is in this example is only for purposes of illustration.

The interior of the pipe is then cleaned and sandblasted. The preformedliner is inserted into the pipe and the pipe is returned to therotomolding machine. The pipe is heated at various temperatures forvarious amounts of time as shown in Table 1 while being rotated aboutone axis. Endcaps are used to contain the tubular liner in the pipe.Such a process leads to adhering a preformed liner to the pipe.Specimens of pipe are subjected to adhesion testing and results areshown in Table 1 below. All of the specimens showed good adhesion above10 lbf/in (1750 N/m), above 20 lbf/in (3500 N/m), and even above 25lbf/in (4400 N/m).

TABLE 1 Example Temperature Hours Load, lb/in. Ex 1-1 720 F. 1 37 Ex 1-2720 F. 1 27 Ex 1-3 740 F. 1 53 Ex 1-4 740 F. 1 40 Ex 1-5 700 F. 2 80 Ex1-6 700 F. 2 84 Ex 1-7 720 F. 2 133 Ex 1-8 720 F. 2 135 Ex 1-9 740 F. 288 Ex 1-10 740 F. 2 120 Ex 1-11 700 F. 3 95 Ex 1-12 700 F. 3 74 Ex 1-13720 F. 3 104 Ex 1-14 720 F. 3 80 Ex 1-15 740 F. 3 107 Ex 1-16 740 F. 3150

Example 2

In this Example, carbon steel pipe is lined using a similar procedure asdescribed in Example 1 with the exception that FP-2 powder is used toform the blended powder containing 1 wt % zinc. Pipes having an ID of 1″are used to form liners with a thickness between 90 mils (2.3 mm) byrotomolding at 700° F. (371° C.) for 60 minutes. Pipes having an ID of4″ (10 cm) are used to form liners with a thickness of about 90 mils(2.3 mm) by rotomolding at 700° F. (371° C.) for 45 minutes.

After the liners are formed and released from the pipes, the pipes aresandblasted as described in Example 1. The preformed liners are insertedinto the pipes and the pipes are returned to the rotomolding machine.For the 1″ (2.5 cm) ID pipes, temperatures ranging between 690° F. (366°C.) and 740° F. (393° C.) are used to heat the pipe with rotation aboutone axis for 60 minutes. For the 4″ ID pipes, temperatures rangingbetween 700° F. (371° C.) and 760° F. (404° C.) for times ranging from40 to 180 minutes are used to heat the pipe with rotation about oneaxis. All pipes are visually inspected by slicing the pipe in half. Thelinings cannot be pried away from the surface of the pipe indicatinggood adhesion of the liner to the pipe.

Example 3

Preformed liners are made by sequentially blending FP-1, FP-2, FP-3,FP-4 and FP-5 with 1 wt % Zn powder and feeding the blends separately toan extruder. The extruder is a commercial extruder manufactured by DavisStandard Division of Compton & Knowles Corporation (Pawcatuck, Conn.),Model # DS 15 HM producing tubular liners having an OD in the range of⅛″ (3.2 mm) to 1″ (25.4 mm) diameter. Small carbon steel pipes having anID ranging from ⅛″ to 1″ diameter are lined after having been cleanedand sandblasted according to the same procedure described in Example 1,matching preformed liners with similar sized pipes by inserting theliners in the pipes and heating the pipes. The pipes are heated at 740°F. (393° C.) with rotation for times varying from 1-3 hours. All pipesare visually inspected by slicing the pipe in half. The linings cannotbe pried away from the surface of the pipe indicating good adhesion ofthe liner to the pipe.

Example 4

Similar to the extrusion method described in Example 4, a preformedliner is extruded from FP 6 blended with 1 wt % zinc and 0.5 wt % micato form a tubular liner of ½″ (12.7 mm) diameter. A small carbon steelpipe with ID of ½″ (12.7 mm) diameter is sandblasted prior to insertingthe tubular preformed liner. The pipe is heated at 740° F. (393° C.)with rotation for 90 minutes. The pipe is visually inspected by slicingthe pipe in half. The lining cannot be pried away from the surface ofthe pipe indicating good adhesion of the liner to the pipe.

The foregoing Examples demonstrate the adherence of the liner of meltprocessible copolymers of TFE of the present invention, as shown by thepeel strength data. Such liners have good or better adherence than pipeslined with ETFE copolymer containing no zinc as well as PFA copolymercontaining zinc which are formed by conventional rotolining techniques.Results emphasize the important commercial improvement in obtaining goodadhering liners by using a more economic process to produce a pipe witha well adhered preformed lining.

1. A tubular preform for lining a pipe and capable of adhering to asurface of the pipe, wherein the tubular preform comprises amelt-processible copolymer of tetrafluoroethylene and perfluoro(alkylvinyl ether), and an effective amount of metal powder to adhere thetubular preform to the surface of the pipe.
 2. The tubular perform ofclaim 1 wherein the metal powder is selected from the group consistingof zinc, copper, and tin, or combinations thereof.
 3. The tubularpreform of claim 1, wherein the metal powder comprises zinc.
 4. Thetubular preform of claim 1, wherein the tubular perform is formed byextruding the melt-processible copolymer of tetrafluoroethylene andperfluoro(alkyl vinyl ether) with the metal powder dispersed therein. 5.The tubular preform of claim 1, further comprising: an inner layer; andan outer layer; wherein the inner layer comprises the metal powderdispersed therein.
 6. The tubular preform of claim 5, wherein the outerlayer is free of metal powder.
 7. The tubular perform of claim 5 whereinthe inner layer and the outer layer comprise the melt-processiblecopolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether). 8.The tubular preform of claim 5, wherein the outer layer consistsessentially of a copolymer of polytetrafluoroethylene andperfluoro(alkyl vinyl ether).
 9. The tubular preform of claim 5, whereinthe tubular preform is formed by co-extruding the inner layer and theouter layer.
 10. The tubular preform of claim 5, further comprising atleast one intermediate layer disposed between the inner layer and theouter layer.
 11. The tubular preform of claim 1, further comprising aplurality of barrier particles.
 12. The tubular preform of claim 10,wherein the at least one intermediate layer comprises a plurality ofbarrier particles.
 13. The tubular preform of claim 11, wherein theplurality of barrier particles is chosen from mica, glass flake, andstainless steel flake.
 14. The tubular preform of claim 10, wherein theplurality of barrier particles is chosen from mica, glass flake, andstainless steel flake.
 15. The tubular preform of claim 1, furthercomprising a plurality of particles for improving the tensileproperties, the elongation properties, wear resistance and/or thermaldissipation of the tubular preform, wherein the particles are chosenfrom ceramic microspheres and aromatic polyamide fibers.
 16. The tubularpreform of claim 1, wherein the tubular preform has a thickness rangingfrom about 20 mils to about 250 mils.
 17. The tubular preform of claim1, wherein the alkyl group of the perfluoro(alkyl vinyl ether) contains1 to 5 carbon atoms.
 18. A pipe with tubular perform of claim 1 adheredto the surface of the pipe with a peel strength of at least 10 lbf/in.